Major General David Hunter, Union commander of the Department of the South, issued the valuable military pass in 1861. It read: "Give her free passage at all times, on all government transports. Harriet… is a valuable woman. She has permission, as a servant of the government, to purchase such provisions from the Commissary as she may need." He was referring to Harriet Tubman, best known as the former slave who became a "conductor" on the Underground Railroad, risking life and liberty to help other runaway slaves escape to freedom. Tubman ran away from her own enslavement in 1849 and immediately had a price on her head. She made the first of thirteen clandestine trips to Maryland to rescue relatives and other slaves in 1850. By 1861, her reputation was widespread. She was smart and strategic, devising clever disguises and playing to her strengths. She operated in winter, when nights were long and people stayed indoors, and made her return trips with the escaped slaves on Saturdays because the papers did not print runaway notices until Mondays. An activist in the Freedman's Aid Society wrote of her in 1865: "She has needed disguises so often, that she seems to have command over her face, and can banish all expression from her features, and look so stupid that nobody would suspect her of knowing enough to be dangerous; but her eye flashes with intelligence and power when she is roused." These experiences not only made Harriet Tubman famous, they made her a valuable asset to the military.

Massachusetts Governor John A. Andrew, a staunch abolitionist, was well-acquainted with Harriet's clandestine efforts and her passion to help. He had a problem: when federal troops occupied regions of South Carolina, Georgia, and Florida, the white plantation owners fled, leaving behind ten thousand slaves who became "contraband of war." They barely had clothes on their backs, much less jobs, money, or education. They flocked to the Union camps, destitute and desperate. Governor Andrew called on Harriet Tubman in the fall of 1861 and asked for her help to go south and help these former slaves adjust to their new way of life and to keep them from overrunning the camps. She agreed, telling a neighbor that he had advised her to act as a "spy, scout, or nurse, as the circumstances required." The governor arranged for her transportation and assigned her to General Hunter, who gratefully accepted her help.

Once in Hilton Head, Harriet began her work as a spy and an organizer and leader of scouts. She selected and paid (out of "secret service money") nine reliable black scouts, riverboat pilots who knew every inch of the local waterways, and trained them in methods of gathering intelligence. Using Harriet's knowledge of covert travel and subterfuge and their familiarity with the terrain, these scouts mapped the shorelines and islands of South Carolina. Harriet and her scouts provided valuable intelligence to the newly-formed black regiments, providing, for example, vulnerabilities and locations of Confederate sentinels. Historian H. Donald Winkler, in his book Stealing Secrets, writes: "Harriet and her nine-man spy team evolved into a kind of special-forces operation for the black regiments. Her team sneaked up and down rivers and into swamps and marshes to determine enemy positions, movements, and fortifications on the shoreline beyond the Union pickets."

Colonel James Montgomery came into Harriet's life they worked together to raise the 2nd South Carolina Colored Infantry regiment. They shared a common vision and passion for the cause and would work together repeatedly on a number of raids. The most famous of Montgomery's river raids was planned and guided by Harriet Tubman herself -- the Combahee River Raid.

When General Hunter asked Harriet if she would go with several gunboats up the Combahee River on a dangerous military mission, she agreed, as long as Montgomery was appointed to command. Hunter agreed; Montgomery led about 300 black soldiers and Harriet led the way. Their mission was to destroy Confederate supply routes and find and disable mines that had been place by Rebels in the river. As a civilian attached to the Army, Harriet had much more leeway than a military commander. She knew that slaves had placed those mines, so she sailed up the river on a reconnaissance mission with her scouts to the slave cabins and found the men who had placed them. She promised freedom to anyone who would help her locate them. If the mission succeeded, she intended to free them all.

On the night of June 1, 1863, Tubman and Montgomery aboard the John Adams, accompanied by another gunboat, sailed silently up the Combahee. Montgomery dispatched troops to scatter the Confederate sentinels at Fields Point while Harriet guided the ships past the mines. The raiders set fire to bridges, plantations, rice mills, and storehouses, seizing cotton, corn, rice, potatoes and supplies -- all reconnoitered by Harriet and her scouts. What couldn't be seized was destroyed. All through the night, while the damage was being done, the gunboats sounded their whistles, a signal to all the slaves within hearing distance to run to the river and the boats that were waiting for them there. More than 700 slaves -- men, women, and children, some with chickens and pigs, answered the call. Harriet said she had never seen anything like it: "They [reminded] me of the children of Israel coming out of Egypt."

Aside from freeing the slaves, the raid was a huge military success that damaged food sources for the Confederacy and opened the river for Union boats that could now cut off further Confederate supplies. It supplied Montgomery with nearly 200 new recruits for his regiment. A Boston newspaper, the Commonwealth, reporting on the Combahee River Raid, said the "gallant band of Black soldiers, under the guidance of a Black woman, dashed into the enemy's country, struck a bold and effective blow, destroying millions of dollars' worth of commissary stores, cotton, and lordly dwellings, and striking terror into the heart of rebeldom… without losing a man or receiving a scratch. It was a glorious consummation." The same paper identified the black woman as Harriet Tubman a month later, thus exposing her work as a spy in a front-page article.

Harriet stayed in the south for the next year, helping in any way she could. Sometimes this meant assisting military regiments, participating in guerrilla activities, or baking and selling pies to help the newly liberated slaves. Through it all, she communicated with her black neighbors, obtaining more intelligence from them than anyone else could, and passing that intelligence on to the commanders for action.